A typical flame detection means at present includes a flame scanner or an industrial camera. Although flame scanners have advantages of high sensitivity and automaticity, there also exit several problems of “miss report, false report and peeking” or the like due to the complexity of the flame detection. Therefore, flame detection by combining an industrial camera with a flame detector could be employed on account of different conditions. A current flame scanner mainly includes an infrared flame scanner and an ultraviolet flame scanner. The infrared flame scanner is typically applied to detecting coal flame, while the ultraviolet flame scanner is typically applied to detecting gas flame and oil flame.
Most furnace burners nowadays adopt a multi-step ignition, and during different phases of the operation, the burning substance is changed. For example, some furnace burners ignite fuel gas or fuel oil and next boost pressure, and then introduce coal for normal operation. Since the characters of radiation spectrums of flames generated by burning different fuel are different, a single infrared or ultraviolet flame scanner cannot meet the requirements of flame detection as to the different operation phases of the burners. Typically, a solution to this problem is to install the infrared and ultraviolet flame scanners simultaneously. However, this will need a very large space to receive a plurality of flame detectors as well as their accessorial lines and conduits, which is rather difficult for those compact furnaces to provide such large spaces.
In addition, the currently used flame scanners and industrial cameras require relatively strict working environments on temperature and pressure. They typically require that the working temperature is below 70° C. and the working pressure is atmosphere or micro negative pressure, otherwise, failure of or damaged to the flame scanner occurs when going beyond above working environments. However, the current flame scanners have to directly face the gas environment inside the furnace chamber. For those high furnace temperature and pressure furnaces, in which the temperature could reach above 1000° C. and the furnace pressure would reach a magnitude of several MPa, the current flame scanners cannot meet the operation requirements under such a high temperature and pressure.
A flame detecting probe is disclosed in Chinese patent publication CN101398183A, which comprises a phototube, an anti-explosion junction cassette, a quartz glass sheet located between a cover for a phototube protecting sleeve and the phototube protecting sleeve, and a cooling venting passage for cooling the phototube and the quartz glass sheet. Such a flame detector probe is mounted inside the furnace chamber. Although the phototube is separated from the high temperature environment inside the furnace via the quartz glass sheet and the cooling venting passage is provided for cooling the phototube, the quartz glass sheet contacts directly with the environment inside the furnace such that the quartz glass sheet and thus the phototube is prone to be damaged by high temperature. Moreover, the furnace has to be shut down when such a flame detector probe is to be replaced.